This invention relates to azo dyes, especially such dyes having utility in black printing inks for ink jet printers. An ink jet printing ink must meet stringent requirements. In particular, in aqueous based systems, it must have up to 8% by weight solubility in water and various organic cosolvents; it must have good water bleed resistance to avoid smeared or blurred printed text or images. It must have the desired jet black shade. It must have low toxicity and have good light fastness and it should be easily manufactured from readily obtained compounds to reduce complexities of synthesis while maintaining low cost.
During ink jet printing, dye at the pen resistor can instantaneously reach about 400.degree. C. causing evaporation of some of the water. Cycling to this temperature can occur at a rate up to about 8,000 times per second. The dye must have low "kogation," i.e., buildup of a plaque on the pen resistor in an ink jet printer must be little or none. Such dyes also should not crust at the pen orifice.
In the case of black dyes used to date for ink jet printing, the dyes have not met all of the requirements as well as desired.
As an example, Food Black 2 has been used in black inks for ink jet printers. Food Black 2 has the formula: ##STR2##
Inks prepared from Food Black 2 certainly have low toxicity and in general give a good jet black color. The water bleed resistance and intercolor bleed resistance of Food Black 2 is tolerable but still not as good as desired and its cost is high.
A major problem with Food Black 2 is that its manufacture requires that Sulfanilic Acid be azo coupled to 1,6 or 1,7 mixed Cleves Acids followed by azo coupling the resulting azo product with RR Acid. Unfortunately RR Acid is a difficult to manufacture and costly intermediate because it is difficult to get the amine group in RR Acid into the .beta. position. As a result the manufacture of RR Acid requires numerous steps, does not usually give good yields when attempted by most persons skilled in the art, and is therefore inefficient and costly.
To avoid the inefficiencies and costs associated with using RR Acid, attempts have been made to make jet black dyes for ink jet printers using Gamma Acid which is much easier to manufacture than RR Acid and is less costly by at least an order of magnitude. Such an attempt has for example been made by making an azo dye using Aminosalicylic Acid azo coupled to 1,6 or 1,7 Cleves Acid or mixtures thereof followed by diazotizing the resulting product and azo coupling to Gamma Acid or a derivative of Gamma Acid. Examples of such dyes are disclosed in U.S. Pat. No. 4,752,337 to Kunde and assigned to Bayer. The reaction, as previously described in U.S. Pat. No. 4,752,337, results in a dye which is unfortunately not nearly as black as desired and which in fact seems to be more nearly a dark brown.
There therefore exists a need for a jet black dye meeting the stringent requirements for ink jet printing while improving its working properties and being easier and less costly to manufacture than Food Black 2.